Binaural technology [1]-[3] is often used to present a virtual acoustic environment to a listener. The principle of this technology is to control the sound field at the listener's ears so that the reproduced sound field coincides with what would be produced when he is in the desired real sound field. One way of achieving this is to use a pair of loudspeakers (electro-acoustic transducers) at different positions in a listening space with the help of signal processing to ensure that appropriate binaural signals are obtained at the listener's ears. [4]-[8]
We discuss hereafter in Section 2 a number of problems which arise from the multi-channel system inversion involved in such a binaural synthesis over loudspeakers. A basic analysis with a free field transfer function model illustrates the fundamental difficulties which such systems can have. The amplification required by the system inversion results in loss of dynamic range. The inverse filters obtained are likely to contain large errors around ill-conditioned frequencies. Regularisation is often used to design practical filters but this also results in poor control performance around ill-conditioned frequencies. Further analysis with a more realistic plant matrix, where the sound signals are controlled at a listener's ears in the presence of the listener's body (pinnae, head . . . ), demonstrates that this is still the case.